This invention relates to flexible cables or flexible printed circuit boards in optical transceivers.
Devices known as optical transceivers are often used to transmit and receive signals in electronic equipment, such as computers and telephone systems. These optical transceivers typically have a laser for generating an output signal that is transmitted through a fiber optic cable, and a detector for receiving a signal from a fiber optic cable. The laser and detector of the optical transceiver, and other electrical components required to operate the optical transceiver must be connected together into an electronic circuit.
The optical transceiver must also include electrical circuit components and mechanical components for mounting and connecting the optical transceiver into the computer or other electronic equipment using the optical transceiver for signal communication. The optical transceivers need to be small in size to fit into the electronic equipment, and yet provide convenient mounting and connection devices to facilitate connection with circuit boards in the electronic equipment by conventional production soldering methods.
The optical transceiver and its associated electronic components generate heat during operation. This heat must sometimes be removed by a heat sink in order to obtain acceptable operating life of the optical transceiver.
Providing the functionality described above, within the tight constraints on the size of the optical transceiver, presents a considerable challenge to designers.
What is needed, therefore, is an improved optical transceiver and method for connecting the transceiver to a circuit board.
Our invention provides an improved optical transceiver having a stiffener including a surface adapted for attachment of a portion of a flexible circuit having electrical components that protrude from the flexible circuit. The surface of the stiffener includes one or more cavities configured for receiving the electrical components that protrude from the flexible circuit.
In one form, the stiffener further includes solder posts for mounting the stiffener on a rigid circuit board of an electronic device incorporating the transceiver. The solder posts may include a shoulder for spacing the stiffener at a predetermined distance from the circuit board of the electronic device.
The portion of the flexible circuit attached to the stiffener may have a first faying surface thereof adapted for attachment to the surface of the stiffener, and a second faying surface thereof bearing solder balls for attachment of the flexible circuit of the transceiver to the rigid circuit board to create an electrical input/output (I/O) interface. The electrical components may be mounted in the cavities in the stiffener and extend through holes in the flexible circuit aligned with the cavities. The electrical components may be electrically attached to the second faying surface with wire bonds. The electrical components may be mounted within the cavities using an electrically and thermally conductive adhesive to thereby provide both an electrical ground and thermal connection between the electrical component and the stiffener.
The stiffener may also include a second surface adapted for attachment to a heat sink. The second surface of the stiffener may include standoffs to space the second surface of the stiffener at a predetermined distance from the heat sink, thereby creating a gap of known width to be filled with a thermally conductive pad or material.
The flexible circuit may include a second portion thereof bearing other electrical components, and having a heat sink surface which can be moved into contact with the heat sink by bending the flexible circuit. The heat sink may be L-shaped with the stiffener being adapted for attachment to the outer surface of one of the legs of the L-shaped heat sink, and the heat sink surface of the flexible circuit being adapted to be attached to the outer surface of the second leg of the L-shaped heat sink.
Our invention also provides a method for constructing an optical transceiver apparatus as described above.
The foregoing and other features and advantages of the invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.